Antibiotic prophylaxis for group B Streptococcus effects largely disappeared by 12 weeks of age in most infants studied.

Compared with infants born vaginally with no exposure to antibiotics, those infants born vaginally with exposure to intrapartum antibiotic prophylaxis for group B Streptococcus had significantly different fecal microbiota immediately following birth, according to results of a recent study published in Scientific Reports. However, by week 12, the differences in gut microbiota were no longer significant between the two groups.

In this longitudinal prospective cohort study, infants born at full-term gestation to women with uncomplicated pregnancies were enrolled from midwifery practices. Fecal microbiomes were compared between infants born vaginally with no antibiotic exposure (n=53), infants born vaginally with intrapartum antibiotic prophylaxis for group B Streptococcus (n=14), and infants born by Cesarean section (n=7) using 16S rRNA Illumina sequencing at 10 days, 6 weeks, and 12 weeks.

Among infants with intrapartum antibiotic prophylaxis exposure prior to vaginal birth, the bacterial community in fecal microbiota was significantly different compared with infants not exposed to antibiotics at 10 days and 6 weeks (P <.05 for both). Intrapartum antibiotic exposure delayed expansion of Bifidobacterium in the first 12 weeks among infants born via vaginal delivery. Longer duration of antibiotic exposure may be associated with a larger effect on Bifidobacterium populations.

By 12 weeks, the bacterial community in fecal microbiota was not significantly different for vaginally born infants exposed to antibiotics. When the duration of intrapartum antibiotic prophylaxis was included in the analysis, infants exposed to the longest duration of antibiotics had significantly different fecal microbiota signatures at 12 weeks.

Infants born via cesarean delivery had significantly different gut microbiota compared with vaginally born infants with no antibiotic exposure at all time points except 6 weeks (P <.05 for all). No differences, however, were reported between the vaginal birth with antibiotics group and the cesarean delivery with antibiotics group, despite different antibiotics used in each group.

According to the study authors, antibiotic prophylaxis for group B Streptococcus "affected all aspects of gut microbial ecology including species richness, diversity, community structure, and the abundance of colonizing bacterial genera. We found that although dramatic at early time points, effects of [intrapartum antibiotic prophylaxis] for [group B Streptococcus] on the microbiome during vaginal birth largely disappeared by 12 weeks of age in most infants."